Thermography is an image-forming process including a heating step and hence includes photothermography in which the image-forming process includes image-wise exposure and direct thermal processes in which the image-forming process includes an image-wise heating step. In direct thermal printing a visible image pattern is produced by image-wise heating of a recording material.
U.S. Pat. No. 3,080,254 discloses a typical heat-sensitive copy paper including in the heat-sensitive layer a thermoplastic binder, e.g ethyl cellulose, a water-insoluble silver salt, e.g. silver stearate and an appropriate organic reductor, of which 4-methoxy-1-hydroxy-dihydronaphthalene is a representative. Localized heating of the sheet in the thermographic reproduction process, or for test purposes by momentary contact with a metal test bar heated to a suitable conversion temperature in the range of about 90–150° C., causes a visible change to occur in the heat-sensitive layer. The initially white or lightly coloured layer is darkened to a brownish appearance at the heated area. In order to obtain a more neutral colour tone a heterocyclic organic toning agent such as phthalazinone is added to the composition of the heat-sensitive layer. Example 2 discloses the use of barbituric acid in heat-sensitive copy sheet to improve the image tone.
WO 96/010213 discloses a thermographic imaging element comprising a substrate having coated on at least one surface thereof a thermographic imaging system comprising at least one layer comprising light-insensitive organic silver salt; reducing agent for silver ion; binder; toner; and a dye which absorbs radiation in the wavelength range of 750–1100 n, wherein said at least one layer comprising said light-insensitive organic silver salt forms an image density greater than about 1.0 when exposed to 0.10 to 2.0 joules/cm2 of said radiation in 0.20 to 200 microseconds. The thermographic imaging system of Examples 2, 3, 5 and 6 contained barbituric acid in association with known toning agents such as phthalazinone and succinimide.
U.S. Pat. No. 3,893,860 discloses in a photothermographic element comprising a support having thereon (I): (a) photographic silver halide in association with (b) a silver salt of a heterocyclic thione, said heterocyclic thione being represented by the formula: wherein R represents atoms completing a 5-member heterocyclic nucleus and Z is alkylene containing 1 to 30 carbon atoms, (c) an organic reducing agent for said silver salt of a heterocyclic thione, and (d) a polymeric, synthetic binder and contiguous to (I), at least one polymer layer (II), the improvement wherein said polymer (A) comprising at least 50% by weight of a polymer (A) comprising the repeating units represented by the formulas: wherein: R1 is hydrogen or alkyl containing 1 to 4 carbon atoms; R2 is an imidazoyl, N-substituted carbamoyl, 2-pyrrolidinyl, acetoacetoxyethoxycarbonyl, acetoacetonylmethylphenyl, ethoxycarbonylaceto, pyridyl, hydroxy, hydroxalkyl containing 1 to 4 carbon atoms, carboxy, carboxyethoxycarbonyl, a heterocyclic ammonium salt group having a 5- or 6-membered azonia nitrogen-containing ring, or a pyridinium salt group, and the weight ratio of starting monomers for said units B and C is, respectively, about 60:40 to 100:0. U.S. Pat. No. 3,893,860 also discloses the use of 2,4-dimercaptopyrimidine as a toning agent for use in photothermographic elements disclosed therein.
EP-A 0 921 433 discloses a thermographic recording element having at least one image forming layer and comprising an organic silver salt, an reducing agent, and at least one of compounds of the following formulas (A) and (B): wherein Z1 and Z2 each are a group of non-metallic atoms capable of forming a 5- to 7-membered ring structure with the carbon atoms, Y1 and Y2 each as —C(═O)— or —SO2—, X1 and X2 each ar a hydroxy or salt thereof, alkoxy, aryloxy, heterocyclic oxy, mercapto or salt thereof, alkylthio, arylthio, heterocyclic thio, amino, alkylamino, is arylamino, heterocyclic amino, acylamino, sulfonamide or heterocyclic group, and Y3 is hydrogen or a substituent. EP-A 0 921 433 also discloses the use of pyrimidine and asymmetric triazines such as 2,4-dihydroxypyrimidine (uracil), 2-hydroxy-4-amino-pyrimidine and azauracil in the thermographic recording element disclosed therein.
U.S. Pat. No. 6,479,227 discloses a thermographic recording element comprising: a support having a pair of opposed surfaces, at least one antistatic layer containing conductive metal oxide particles and at least one thermographic recording layer containing an organic silver salt and a reducing agent on the first surface of the support, and at least two layers on the other surface of the support, wherein the outermost layer of said at least two layers contains a hydrophobic polymer binder and at least one layer of said at least two layers other than said outermost layer contains a matte agent, wherein: said conductive metal oxide particles are acicular particles having a major axis to minor axis ratio of from 3/1 to 50/1, and said thermographic recording element further comprises a nucleating agent. U.S. Pat. No. 6,479,227 also discloses the use of 2,4-dimercaptopyrimidine, pyrimidine and asymmetric triazines such as 2,4-dihydroxypyrimidine (uracil), 2-hydroxy-4-amino-pyrimidine, azauracil, 4-hydroxy-2-mercaptopyrimidine, 2-mercaptopyrimidine, 4,6-diamino-2-mercaptopryimidine, and 2-mercapto-4-methylpyrimidine hydrochloride in the thermographic recording element disclosed therein.
U.S. Pat. No. 3,951,660 discloses a photographic radiation sensitive recording material having therein a radiation sensitive composition and at least one layer containing dispersed in a binding agent a substantially non-light sensitive silver salt, a reducing agent for the non-light sensitive silver salt, and a toner compound, the improvement which comprises the toner being a heterocyclic toner compound of the following formula: in which X represents O or N—R5; R1, R2, R3 or R4 represent hydrogen, alkyl, cycloalkyl, alkoxy, alkylthio, hydroxy, dialkylamino or halogen, in addition to which R1 and R2 or R2 and R3 or R3 and R4 can represent the ring members required to complete an anellated aromatic ring, and R5 represents alkyl. U.S. Pat. No. 3,951,660 discloses 2,4 (1H,3H)-quinazolinedione and various 2,4 (1H,3H)-quinazolinedione (benzoyleneurea) derivatives substituted at the nitrogen atom in the 1-position i.e. 2-hydroxy-pyrimidine derivatives annelated at the 5,6 positions with a benzene ring:
Compoundnr.11-methyl-2,4(1H,3H)-quinazolinedione 21,7-dimethyl-2,4(1H,3H)-quinazolinedione 31-ethyl-2,4(1H,3H)-quinazolinedione 41-butyl-2,4(1H,3H)-quinazolinedione 51-butyl-8-methyl-2,4 (1H,3H)-quinazolinedione 81-butyl-7-methyl-2,4 (1H,3H)-quinazolinedione 262,4 (1H,3H)-quinazolinedione 381-isobutyl-2,4(1H,3H)-quinazolinedioneINVENTION EXAMPLES are disclosed in U.S. Pat. No. 3,951,660 in which the use of compounds 1, 3 and 26 as toning agents in thermographic recording materials is exemplified.
U.S. Pat. No. 3,885,967 discloses a photosensitive material for a thermally developable lightsensitive element which comprises: a) a silver salt component comprising silver laurate or silver caprate, b) a catalytic amount of a photosensitive silver halide component comprising a photosensitive silver halide, or a compound which reacts with silver laurate or silver caprate to form a photosensitive silver halide, c) a reducing agent, d) a binder, and e) a toning agent comprising a compound represented by the formula: wherein R1, R2, R3 and R4 each represents a hydrogen atom, an alkyl group, an aryl group, an acylamido group, a halogen atom, a hydroxyl group or a nitro group.
EP-A 0 752 6-16 discloses a thermographic material comprising at least one element and wherein said element(s) contain(s) therein a substantially light-insensitive organic heavy metal salt and an organic reductor therefor, the said material being capable of thermally producing an image from said organic heavy metal salt and reductor, wherein said material contains a 1,3-benzoxazine-2,4-dione toning agent having general formula (I): wherein R1 represents hydrogen, —CH2OH, —(C═O)—R, —CONHR, or M; R2, R3, R4 and R5 each independently represents hydrogen, —O—(C═O)—OR or —NH—(C═O)—OR and at least one of which is not hydrogen if R1 is also hydrogen; R represents an alkyl or aryl group either of which may be substituted; and M represents a monovalent heavy metal ion.